The discs in between the vertebral bodies are composed of two main parts: the outer layers being the annulus fibrosis and the inner material known as the nucleus pulposus. The annulus is tough and is arranged in layers rather similar to an onion, with the successive layers angled slightly differently to their neighbours to allow good strength in many orientations. The annular layers attach through the bones above and below, anchoring them firmly and meaning a disc cannot in reality slip out. Nerve endings giving both positional and pain information are present in the outermost layers of the annulus.
The more fluid nucleus part of the disc is surrounded by the inner layers of the annulus which support it and allow strength under compression. A normal disc is made up of about sixty-five percent nucleus which is able to sustain three-quarters of the disc load. The nucleus contains macromolecules which can attract and hold two and a half times their weight in water, the nucleus being made up of 90% water until we approach our thirties and it declines to around 65% four decades later. The outer third of the disc annulus receives a blood supply while the rest does not and must depend on the nutrients and water diffusing across from the vertebrae above and below for nutrition.
The annulus can be stressed repeatedly by loading and twisting forces which cause microscopic trauma to the fibres and result in annular tears developing. Circumferential tears track around the disc between the layers and radial tears cross the layers from inside to out, with a combination of these tears sometimes developing into larger splits from the inside nuclear material to the exterior. This can permit extrusion of the disc material out of the disc and inflammation or compression of the exiting nerve roots, leading to severe leg pain known as sciatica.
In the first twenty years of life 80 to 90% of the weight applied to the spine is transmitted across the back third of the disc. However, as degenerative changes occur and the discs lose height, the axis of stresses moves backwards and loads the facet joints more severely. The facet joints can react to this by increasing in size with arthritic changes and by developing osteophytes. These processes can progress to narrowing the central canal and the nerve exit routes, compressing the central nervous tissues or the nerve roots and causing leg and back pain. Later in life this progresses to spinal stenosis which can give various symptoms and sometimes requires operation.
The intervertebral disc and other spinal structures around the spinal segments have been shown to be potential causes of pain. Direct stimulation of the outer layers of the disc has been shown to produce pain in a proportion of patients undergoing operation. The large water attracting molecules break into smaller molecules as the disc ages and repair of this process is slow. The tears and fissures in the annular fibres increase the gradual breakdown and dehydration of the disc structure, with the poor blood supply to the outer disc layers insufficient to prevent the continuing internal disc degeneration.
The poor blood supply through the endplates of the vertebrae may be related to spinal pain problems but the ability to correlate the degenerative changes to the patient's pain symptoms is problematical and cannot usually be connected with any certainty. This makes attribution of a cause and so the probability of therapeutic success difficult.
Pain problems in the intervertebral discs may also involve biochemical and other factors and a lower pH has been found in painful as compared to non painful discs. In animal studies reduction in the pH of the discs heightens pain reactions and increases the pain behaviour of the creatures. Increased neuropeptide levels have been produced in the experimentally deformed discs of animals and could be involved in modulation and transmission of pain in the central nervous system. Mechanical stresses, micro-trauma and biochemical changes may increase production of inflammatory chemicals and enzymes which can breakdown tissues. These factors may all increase the disc and other spinal structure changes. - 14130
The more fluid nucleus part of the disc is surrounded by the inner layers of the annulus which support it and allow strength under compression. A normal disc is made up of about sixty-five percent nucleus which is able to sustain three-quarters of the disc load. The nucleus contains macromolecules which can attract and hold two and a half times their weight in water, the nucleus being made up of 90% water until we approach our thirties and it declines to around 65% four decades later. The outer third of the disc annulus receives a blood supply while the rest does not and must depend on the nutrients and water diffusing across from the vertebrae above and below for nutrition.
The annulus can be stressed repeatedly by loading and twisting forces which cause microscopic trauma to the fibres and result in annular tears developing. Circumferential tears track around the disc between the layers and radial tears cross the layers from inside to out, with a combination of these tears sometimes developing into larger splits from the inside nuclear material to the exterior. This can permit extrusion of the disc material out of the disc and inflammation or compression of the exiting nerve roots, leading to severe leg pain known as sciatica.
In the first twenty years of life 80 to 90% of the weight applied to the spine is transmitted across the back third of the disc. However, as degenerative changes occur and the discs lose height, the axis of stresses moves backwards and loads the facet joints more severely. The facet joints can react to this by increasing in size with arthritic changes and by developing osteophytes. These processes can progress to narrowing the central canal and the nerve exit routes, compressing the central nervous tissues or the nerve roots and causing leg and back pain. Later in life this progresses to spinal stenosis which can give various symptoms and sometimes requires operation.
The intervertebral disc and other spinal structures around the spinal segments have been shown to be potential causes of pain. Direct stimulation of the outer layers of the disc has been shown to produce pain in a proportion of patients undergoing operation. The large water attracting molecules break into smaller molecules as the disc ages and repair of this process is slow. The tears and fissures in the annular fibres increase the gradual breakdown and dehydration of the disc structure, with the poor blood supply to the outer disc layers insufficient to prevent the continuing internal disc degeneration.
The poor blood supply through the endplates of the vertebrae may be related to spinal pain problems but the ability to correlate the degenerative changes to the patient's pain symptoms is problematical and cannot usually be connected with any certainty. This makes attribution of a cause and so the probability of therapeutic success difficult.
Pain problems in the intervertebral discs may also involve biochemical and other factors and a lower pH has been found in painful as compared to non painful discs. In animal studies reduction in the pH of the discs heightens pain reactions and increases the pain behaviour of the creatures. Increased neuropeptide levels have been produced in the experimentally deformed discs of animals and could be involved in modulation and transmission of pain in the central nervous system. Mechanical stresses, micro-trauma and biochemical changes may increase production of inflammatory chemicals and enzymes which can breakdown tissues. These factors may all increase the disc and other spinal structure changes. - 14130
About the Author:
Jonathan Blood Smyth, editor of the Physiotherapy Site, writes articles about Physiotherapists, physiotherapy, physiotherapists in Birmingham, back pain, orthopaedic conditions, neck pain and injury management. Jonathan is a superintendant physiotherapist at an NHS hospital in the South-West of the UK.
No comments:
Post a Comment